The present invention generally relates to an apparatus and method for semiconductor processing and more particularly, relates to a closed-loop controlled apparatus and method for preventing contamination in a semiconductor process chamber which includes an exhaust vent mounted to the process chamber such that the chamber may be continuously pumped during wafer loading and unloading, the vent is equipped with a reduced cross-sectional area for achieving increased fluid flow rate and a butterfly valve for adjusting the flow rate through the exhaust vent and for detecting when the vent is blocked by contaminating particles.
In semiconductor processing, a large portion of the yield losses can be attributed to contaminations by particles and films of various nature. The contaminants may be organic or inorganic particles, films formed of polymeric bases, or other ionic based materials. The particles or films may be generated as byproducts in the reaction of reactant gases, by the surrounding environment, by the processing equipment or by the handling of manufacturing personnel. Some contaminants are particles or films generated from condensed organic vapors, solvent residues, photoresist or metal oxide compounds.
Typical problems and the detrimental effects caused by particle or film contaminants are poor adhesion of deposited layers, poor-formation of LOCOS oxides, or poor etching of the underlying material. The electrical properties and the stability of devices built on the semiconductor substrate may also be seriously affected by ionic based contaminants. The various forms of contaminants therefore not only reduce the product yield but also degrades the reliability of the devices built. For instance, contaminant particles can cause a device to fail by improperly defined patterns, by creating unpredictable surface topography, by inducing leakage current through a insulating layer, or otherwise reducing the device lifetime. It is generally recognized that a particle contaminant that exceeds one-fifth to one-half of a minimum feature size on a device has the potential of causing a fatal defect, i.e. a defect that causes a device to fail completely. A defect of smaller size may also be fatal if it falls in a critical area, for instance, a particle contaminant in the gate oxide layer of a transistor. In modern high density devices, such as a dynamic random access memory chip, the maximum allowable number of particle contaminants per unit area of the device must be reduced accordingly in order to maintain an acceptable yield and reliability.
One of the widely used processing techniques for semiconductor wafers is a low pressure chemical vapor deposition (LPCVD) technique. A LPCVD process can be carried out in an apparatus such as that shown in FIG. 1. The LPCVD method has been widely used in the deposition of silicon nitride or TEOS oxide films on semiconductor wafers. In the method, a gas containing the structural elements of the film material to be formed is first fed into a chamber, followed by heating the gas mixture to induce a chemical reaction to deposit the desired film on the semiconductor substrate. In a conventional CVD method, a silicon nitride film can be deposited by a chemical reaction between silane (SiH4) and ammonia (NH3) at 1 ATM and a temperature of 700xcx9c900xc2x0 C., or by a mixture of dichlorosilane (SiCl2H2) and ammonia at a reduced pressure and a temperature of 700xcx9c800xc2x0 C.
As shown in FIG. 1, reactant gases of dichlorosilane 12 and ammonia 14, each carried by a carrier gas of nitrogen, are fed into the process chamber 18 through the inner tubes 40. The reaction gases are mixed at the bottom portion of inner tubes 40. Manifold 16 provides inlets and outlets for the gases and is used as a pedestal support for the inner tubes 40 and the outer tubes 24. The process chamber 18 is first evacuated by vacuum pump 20 prior to the reaction. A purge gas of nitrogen 22 is then used to fill the process chamber 18 and to drive out any residual gas left from the previous deposition cycle. A cold trap 26 maintained at sub-ambient temperature, e.g., of approximately 12xcx9c18xc2x0 C., is used in the vacuum line to trap particles that cannot be pumped away. The manifold 16 is provided with a pressure sensor 28 which is connected via a conduit 30 to the manifold 16 at a pressure port 32. A main valve 34 and pressure switches (not shown) are provided in the vacuum evacuation line for controlling the fluid flow. A vent line 48 is connected to the vacuum evacuation line for venting spent reactant gases through control valves 52 and 54 to the exhaust vent 56.
After the reactant gases of SiCl2H2 and NH3 are mixed in the inner tube 40, the gas mixture is flown into the process chamber 18 to deposit silicon nitride films on wafers held in a wafer boat (not shown). It has been observed that during the reaction between SiCl2H2 and NH3, a reaction byproduct of NH4Cl is frequently produced. The ammonium chloride powder which is in a very fine powdery form causes a defect on the wafer surface known as nitride haze. It is believed that during a nitride deposition process, contaminating powder may be coated inside the conduit between the chamber 18 and the cold trap 26, inside the conduit between the cold trap 26 and the gate valve 34, inside the gate valve 34, and inside the conduit between the gate valve 34 and the automatic pressure controller 20. The powdery contaminant may then be siphoned back into the process chamber 18 during an unintentional back-flow process. The fine powder of ammonium chloride deposits on top of a wafer surface and forms a haze defect. The nitride haze, once formed, is very difficult to remove from the wafer surface. For instance, a wet scrubbing method by using a brush cannot remove the haze from the wafer surface. The nitride haze acts as an additional insulating layer on top of the silicon wafer and presents processing difficulties in subsequently carried out processes. One of such processing difficulties occurs in the formation of LOCOS oxide insulation. The nitride haze impedes the growth of LOCOS oxide. Similar contaminants have also been observed in a TEOS oxide deposition process with similarly undesirable results.
In an effort to reduce or eliminate the nitride haze problem, a bypass vent pipe has been used to bypass the gate valve and to provide continuous pumping of the chamber during wafer loading and unloading steps. Even though this method reduces somewhat the magnitude of the chamber contamination problem, the small vent tube used for bypassing the gate vale is frequently plugged with the contaminating particles. The cleaning of such tubes becomes a time and labor consuming process during a preventive maintenance procedure. It is therefore desirable to have a bypass vent pipe for use in such application that does not get plugged up and furthermore, it would be desirable to have a vent pipe that is capable of indicating when such blockage occurs so that the vent pipe may be serviced.
It is therefore an object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber that does not have the drawbacks or shortcomings of the conventional apparatus of a vent tube.
It is another object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber that utilizes an exhaust vent for bypassing a gate valve such that the chamber may be continuously pumped during wafer loading and unloading to prevent a back-flow of contaminating particles into the chamber.
It is a further object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber by utilizing an exhaust vent equipped with a reduced cross-sectional area such that a fluid flow rate through the area is significantly higher than through the other areas of the vent in order to prevent the cumulation of contaminating particles in the exhaust vent.
It is another further object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber which includes an exhaust vent that has conduits of large cross-sectional area connected by a conduit of small cross-sectional area such that any cumulation of a fine powdery ammonium chloride material in the exhaust vent can be avoided.
It is still another object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber which includes an exhaust vent that is equipped with a large diameter cross-sectional area and a butterfly valve contained therein for adjusting the fluid flow rate through the conduit.
It is yet another object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber which includes an exhaust vent that is equipped with a butterfly valve for controlling a fluid flow rate through the vent and for feeding back a signal to a controller such that the operation of the deposition chamber can be shut off when the angle of the butterfly valve exceeds a pre-set value.
It is still another further object of the present invention to provide a closed-loop controlled method for preventing contamination to a low pressure chemical vapor deposition chamber incorporating the steps of connecting an exhaust vent to the process chamber and equipping a conduit of the vent with a butterfly valve for adjusting a fluid flow rate through the conduit.
It is yet another further object of the present invention to provide a closed-loop controlled method for preventing contamination to a low pressure chemical vapor deposition chamber that utilizes an exhaust vent with a butterfly valve installed therein for adjusting a fluid flow rate and sending out a signal to a controller such that the operation of the deposition chamber can be shut off when the angle of the butterfly valve detected exceeds a pre-set value.
In accordance with the present invention, a closed-loop controlled apparatus and method for preventing contamination to a low pressure chemical vapor deposition chamber incorporating the use of an exhaust vent which has a reduced cross-sectional area therein and a butterfly valve installed in the vent for adjusting the fluid flow rate through the vent are disclosed.
In a preferred embodiment, a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber can be provided which includes a chamber equipped with a vacuum port in fluid communication with a gate valve and a vacuum pump; an exhaust vent connected to the vacuum port and the vacuum pump in parallel with and bypassing the gate valve, the vent includes a first conduit and a second conduit connected in fluid communication with a middle conduit thereinbetween, the first conduit and the second conduit each has an internal diameter larger than the internal diameter of the middle conduit, and a pneumatic valve positioned in the middle conduit adapted for turning on or off the exhaust vent; a butterfly valve situated in the second conduit for adjusting a fluid flow rate through the conduit and sending out a signal to a controller indicating an angle of the valve; and a controller for shutting down the deposition chamber when the angle exceeds a pre-set value.
The closed-loop controlled apparatus may further include a cold trap connected in series and in fluid communication with the gate valve. The pneumatic valve is turned on during wafer loading and unloading processes into and out of the deposition chamber with the vacuum pump operating. The pre-set value of the angle of the butterfly valve is at least 60xc2x0 as measured from a vertical axis. The first conduit and the second conduit each has an internal diameter at least two times the internal diameter of the middle conduit. The pneumatic valve may be a normal-closed air actuated valve. The first conduit and the second conduit may each have an internal diameter four times the internal diameter of the middle conduit.
The low pressure chemical vapor deposition chamber may be a silicon nitride deposition chamber or a TEOS oxide deposition chamber. The exhaust vent is turned on during wafer loading and unloading such that reaction by-products produced in the deposition chamber can be carried away by the vacuum pump. The deposition chamber may be a silicon nitride deposition chamber which generates a reaction by-product of NH4Cl. A fluid flow rate in the middle conduit when the vacuum pump is operating is at least four times the fluid flow rate in the first and second conduit. A fluid flow rate in the middle conduit is higher than a fluid flow rate in the first and second conduit such that reaction by-products from the chamber does not cumulate in the conduit. The fluid flow rate in the middle conduit may be sufficiently high such that reaction by-products from the deposition chamber does not cumulate in the pneumatic valve. The exhaust vent operates to prevent any reaction by-products deposited in the first, second and middle conduit from being back-flowed into the deposition chamber.
The present invention is further directed to a closed-loop controlled method for preventing contamination to a low pressure chemical vapor deposition chamber which can be carried out by the operating steps of first providing a chamber equipped with a vacuum port in fluid communication with a gate valve and a vacuum pump; then connecting an exhaust vent in parallel with and bypassing the gate valve with a first conduit of the device connected to the vacuum port, a second conduit of the device connected to the vacuum pump and a middle conduit providing fluid communication between the first and the second conduit equipped with a pneumatic valve, the second conduit is equipped with a butterfly valve for adjusting a fluid flow therethrough; then turning on the pneumatic valve with the vacuum pump operating in loading/unloading at least one wafer into/from the deposition chamber; and adjusting an angle of the butterfly valve by a controller such that a pre-set fluid flow rate through the second conduit is maintained.
The closed-loop controlled method for preventing contamination may further include the step of providing the exhaust vent with a first and second conduit each has an internal diameter at least two times that of the middle conduit. The method may further include the step of shutting down the deposition chamber when the angle of the butterfly valve exceeds a pre-set value. The method may further include the step of providing the exhaust vent with a middle conduit smaller than the first and second conduit such that a sufficiently higher fluid flow rate can be generated in the middle conduit for preventing cumulation of reaction by-products in the middle conduit.
The closed-loop controlled method may further include the step of conducting a nitride deposition process on the at least one wafer or conducting a TEOS oxide deposition process on the at least one wafer. The method may further include the step of providing the exhaust vent with a first and second conduit each has an internal diameter at least two times that of the middle conduit. The method may further include the step of providing the pneumatic valve in a normal-closed air actuated valve. The method may further include the step of turning on the exhaust vent during wafer loading and unloading to carry away reaction by-products generated in the deposition chamber by a vacuum pump. The method may further include the step of turning on the exhaust vent during wafer loading and unloading to carry away ammonium chloride powder generated in a nitride deposition chamber by a vacuum pump. The method may further include the step of generating a fluid flow rate in the middle conduit that is sufficiently high such that reaction by-products from the deposition chamber do not cumulate in the pneumatic valve, and the step of preventing any reaction by-products deposited in the first, second and middle conduit from being back-flowed into the deposition chamber.
The present invention is further directed to a closed-loop controlled method for preventing contamination to a low pressure chemical vapor deposition chamber which includes the steps of first providing a chamber equipped with a vacuum port in fluid communication with a gate valve and a vacuum pump; then connecting an exhaust vent in parallel with and bypassing the gate valve with a first conduit of the device connected to the vacuum port, a second conduit of the device connected to the vacuum pump and a middle conduit providing fluid communication between the first and second conduit equipped with a pneumatic valve, the second conduit is equipped with a butterfly valve for adjusting a fluid flow therethrough; then turning on the pneumatic valve with the vacuum pump operating and loading/unloading at least one wafer into/from the deposition chamber; then detecting the fluid flow rate through the second conduit and an angle of the butterfly valve by a controller and shutting down the deposition chamber when the angle of the butterfly valve detected exceeds a pre-set value.
The closed-loop controlled method may further include the step of shutting down the deposition chamber when the angle of the butterfly valve detected exceeds 60xc2x0 as measured from a vertical axis. The method may further include the step of wet cleaning the first, second and middle conduit of the exhaust vent and removing all contaminating particles on interior walls of the conduits when the pre-set value of the angle of the butterfly valve is detected.